title: Two-dimensional heterospectral correlation analysis of water and liquid oleic acid using an online near-infrared/mid-infrared dual-region spectrometer.
abstract: Two-dimensional (2D) near-infrared (NIR) and mid-infrared (mid-IR) heterospectral correlation analyses were used to characterize temperature-dependent spectral variations of water and liquid oleic acid (OA), utilizing a dataset obtained with an online NIR/mid-IR dual-region spectrometer. The spectrometer facilitated sequential acquisition of both NIR (10 000-4000 cm(-1)) and mid-IR (5000-1200 cm(-1)) spectra, which compose the spectral dataset required for 2D NIR/mid-IR heterospectral correlation analysis. Both NIR and mid-IR spectra were obtained under the same conditions by using the same sample compartment, more quickly and easily than is possible when using existing spectrometers. Successful 2D NIR/mid-IR correlation analysis was performed with the data collected with this instrument to characterize the temperature dependence of the molecular structures of water and pure liquid OA. Temperature-induced NIR/mid-IR spectral changes for water and OA were analyzed in detail, and band assignments in the NIR and mid-IR regions were elucidated by 2D NIR/mid-IR heterospectral correlation analysis. The results of this study indicate that liquid water consists of two major species, strongly hydrogen-bonded species and weakly hydrogen-bonded species, as well as one minor species. Additionally, OA was found to form an intermolecularly hydrogen-bonded species in which a single hydrogen bond of the dimer was broken; a mid-IR band at 1724 cm(-1) was assigned to this species. Moreover, 2D NIR/mid-IR heterospectral correlation analysis revealed that NIR bands at 4690 and 4644 cm(-1) also arose from intermolecularly hydrogen-bonded species. These results demonstrate that 2D NIR/mid-IR heterospectral correlation analysis is useful not only for NIR band assignments, but also for molecular structure studies. The spectrometer we developed makes this analysis even more accessible.
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan. takuma.fm@u.tsukuba.ac.jp
authors.forename: Takuma
authors.initials: T
authors.lastname: Genkawa
authors.forename: Masahiro
authors.initials: M
authors.lastname: Watari
authors.forename: Takashi
authors.initials: T
authors.lastname: Nishii
authors.forename: Masao
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Ozaki